Anglo concertina - name given to several types of Concertina
The anglo concertina (or to give it its original name, the Anglo-German concertina) was developed soon after the English, using as a model the diatonic German instruments which were also the ancestors of the melodeon and harmonica. It can have two or three curved rows of buttons on each side and a wrist strap for support. Some duet systems can look a bit like an anglo, but the firm diagnostic test is "if I press a button, do I get the same note when I close the bellows as when I open them". If the answer is "no, I get different notes" then it is an anglo. Only the anglo of all the main types of concertina plays different notes on the push and on the pull.
(It has been pointed out that occasionally English and duet concertinas can be so horrendously out of tune as to play very different notes on the pull from the push, and thus fool the unwary into thinking that they are anglos. This is, fortunately, very rare).
On two-row anglos each row is in a different key, so the instrument is capable of playing in two major keys only. The three row is the same, except that the third outside row is a collection of assorted accidentals that enable the skilled player to play in other keys (thus giving rise to the full name of the instrument, the anglo-chromatic concertina). The low notes on all anglos are on the left hand side, and the high notes on the right.
Anglos are referred to by the keys of the middle and inner rows. The most common is the C/G anglo, where the outside row (or middle row on a three row) plays the key of C and the inside row plays the key of G. Also fairly common are G/D instruments, commonly used for English dance music. Normally the two rows are a fifth apart, so that you can have other tunings such as Bb/F and Ab/Eb. Very occasionally you find C/C#, which is chromatic between the two main rows, and a whole variety of odd tunings made to the request of the purchaser.
Anglos are also referred to by the number of buttons they have:- a 20-button is a two-row, a 30-button is a three row, a 40-button is also a three row but with additional buttons dotted around to make playing in different keys or more smoothly a little bit easier. You can also find anglos with 26, 38, 45 or more buttons. You can play good music on a 20-button instrument, but it is limiting - you have to fudge any accidentals you encounter. 30-button concertinas are fine for all normal use. When you get into the expert bracket look for a 40-button.
If you're getting the picture that there is a lot of variation amongst different anglos you'd be right!
The 3-CD set Anglo International (Folksound Records, 2005) presents some two dozen players from around the world, and shows the great variety of styles that can be achieved on this essentially unsophisticated instrument. See http://www.angloconcertina.co.uk/
The anglo was taken up by musicians in many parts of the world - in Europe, America and by both blacks and whites in South Africa.
The instrument became very popular in Irish traditional music - William Mullaly is thought to be the first Irish player to have been recorded; more recent traditional exponents include Bernard O'Sullivan, Tommy McMahon, Chris Droney, John Kelly and Packie Russell. Notable modern players include Noel Hill.
Recordings of traditional English musicians are rare - the most important examples are by Scan Tester and William Kimber. John Kirkpatrick is the most prominent player to have come out of the post-war English folk revival.